Dynamic Cast

'dynamic_cast' is exclusively used with pointers and references to objects. It allows any type-casting that can be implicitly performed as well as the inverse one when used with polymorphic classes, however, unlike static_cast, dynamic_cast checks, in this last case, if the operation is valid. That is to say, it checks if the casting is going to return a valid complete object of the requested type.

Checking is performed during run-time execution. If the pointer being casted is not a pointer to a valid complete object of the requested type, the value returned is a 'NULL' pointer.

Code:

class Base { virtual dummy() {} };
class Derived : public Base {};

Base* b1 = new Derived;
Base* b2 = new Base;

Derived* d1 = dynamic_cast(b1); // succeeds
Derived* d2 = dynamic_cast(b2); // fails: returns 'NULL'